Cancer is a disease that accounts for a large proportion of causes of death in contemporary Japanese. A variety of anticancer agents have been developed and practically used so far, but the anticancer agents have strong side effects, and their burden to the bodies of patients is large. In recent years, heavy particle radiotherapy has been practically used, but the cost of the therapy is high, and the therapy is available only in limited facilities. Thus, heavy particle radiotherapy cannot be said to be a general option that can be freely selected at present. Therefore, anticancer agents which are highly effective against cancer, have only small side effects, and can be provided at low cost, are still strongly demanded.
As an example of a low-cost anticancer agent, an antitumor agent containing as an effective ingredient an antiallergic agent oxatomide or azelastine, or a pharmaceutically acceptable salt thereof, is disclosed in Patent Document 1. Both oxatomide and azelastine are agents classified as histamine H1 receptor antagonists. The antitumor uses of oxatomide and azelastine and pharmaceutically acceptable salts thereof described in Patent Document 1 are, more specifically, therapeutic uses for malignant tumors. Patent Document 1 does not disclose at all that leukotriene inhibitors such as leukotriene receptor antagonists are actually effective for various epithelial and nonepithelial tumors which have been spontaneously developed in vivo while producing few side effects. Patent Document 1 also does not disclose an effect on benign tumors. Moreover, Patent Document 1 does not at all describe actions of oxatomide and azelastine on stromal components such as nerves, blood vessels, and fibroblasts in tumor sites.